Device for placing a receiving part onto a head of a bone anchoring element

ABSTRACT

A device for placing a receiving part of a bone anchoring device onto a head of a bone anchoring element, comprising: a holding device, a collet having a longitudinal axis and being held by the holding device, wherein the collet includes a distal end portion configured to be flexibly expanded and/or compressed in a radial direction perpendicular to the longitudinal axis, wherein an engagement feature is provided at an outer contour of the distal end portion of the collet configured to engage a portion of an inner wall formed in a rod receiving channel or a bore of a receiving part.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present disclosure claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/953,510, filed on Mar. 14, 2014, the contents ofwhich are hereby incorporated by reference in their entirety, and claimspriority to European Patent Application EP 14160126.0, filed on Mar. 14,2014, the contents of which are hereby incorporated by reference intheir entirety.

BACKGROUND

1. Field of the Invention

The present invention relates to a device for placing a receiving partof a bone anchoring device onto a head of a bone anchoring element. Thepresent invention further relates to such a receiving part of a boneanchoring device. The device comprises a holding portion, a collet forengaging the receiving part and a corresponding engagement feature.

Fractures of the spinal column, arthrodesis, scoliosis, etc. are oftentreated by stabilizing the spinal column using bone anchors applied totwo or more vertebrae and connecting these via rigid or dynamicallyflexible stabilization rods such as to define a predetermined relativeposition and movement tolerance for each of the vertebrae involved. Inoperation, vertebrae are first selectively supplied with bone anchorsand a stabilization rod is then attached to connect each of the boneanchors. The connection is established by means of a receiving part,which connects to a head of the bone anchoring element and receives aspinal rod in a rod receiving channel thereof.

In recent years, there has been a tendency to assemble such boneanchoring devices in situ. Methods of in situ assembling of the boneanchoring devices advantageously allow—since the receiving parts areattached to the bone anchors in a subsequent step—visual inspection ofseveral structures in place such as particularly neurological structuresetc., which may be critical. New clinical methods and surgical stepsalso become possible. Moreover, particular advantages arise in that apreparation of very small MIS (minimally invasive surgery) accesses ismade possible.

For example a bone anchoring element is anchored in a vertebra first,whereafter a receiving part is placed onto the head of the boneanchoring element. However, such construction necessitates that thereceiving part allows a function to load the head from the bottom. As aconsequence, the bottom opening has an increased diameter and the headhas to be received by a portion of pressure element or inner capprovided within the receiving part, which allows encompassing the headand locking against a seat formed adjacent the bottom opening. One earlyexample is described in document U.S. Pat. No. 6,471,705 A, or EP 1 105057 A1, by applicant.

In view of the above, a need has arisen to also provide a devicesuitable for placing a receiving part onto a head of a bone anchoringelement.

2. Description of the Related Art

Document US 2011/0166606 A1 discloses a reduction tool designed toengage a body portion having a rod receiving channel and to insert aspinal rod therein. The tool comprises an outer tube having engagementfeatures at the distal end and two opposite slots through which the rodis inserted, and an inner tube which advances a locking cap and the rod.At the proximal end, the outer tube also has two opposite slots suchthat a pivot point is formed in a middle portion wherein a compressionof the proximal end of the outer tube results in an expansion of thedistal end. As a consequence of such manipulation, engagement of thereceiving part by means of protruding engagement features provided atthe distal end of the outer tube can be facilitated. Upon engagement,those protrusions are led into corresponding recesses formed in an outercircumferential surface of the receiving part.

However, the above described reduction tool is configured to engage areceiving part in a state preassembled with the bone anchoring element,and further, due to the pivoting expansion to engage and disengage thereceiving part at its circumferential surface, much space is need in apatient's body rendering the tool less suitable for minimal invasivesurgery and in situ operation.

Document US 2012/0296171 A1 discloses an inserter including a driver anda receiver member wherein a head of a bone anchor to be inserted issecurely connected to the inserter by virtue of the receiver memberwhich is used in a collet-like fashion. The receiver member therebyreceives the head and a cylindrical body is slid over a conical portionof the receiver member to compress deflectable flanges onto the head. Adriving operation may then be performed with regard to the bone anchor.In this embodiment, however, the receiver member is part of the inserterand cannot be released and used to receive a rod.

SUMMARY

It is thus an object to provide a device for placing a receiving partonto a head of a bone anchoring element, which improves known methodsand devices.

The object is solved by a device for placing a receiving part of a boneanchoring device onto a head of a bone anchoring element according toclaim 1. The object is also solved by a receiving part for connecting abone anchoring element having a head and a shank to a spinal rodaccording to claim 15. Advantageous aspects and embodiments becomeapparent from the dependent claims.

The device includes a holding device and a collet held by the holdingdevice. The collet has a distal end portion which is configured to beflexibly expanded and/or compressed, which allows engaging and/ordisengaging a corresponding receiving part. An engagement feature isprovided at an outer contour, or outer surface, of the distal endportion of the collet. The engagement feature may engage a portion of aninner wall formed in a rod receiving channel or in a bore of a receivingpart.

More specifically, the engagement feature is not provided at an innersurface of a tube or shaft as proposed in prior art, but on its outersurface such as to engage an inner wall of the receiving part. The innerwall may be that of the inner bore extending for example from a top endto the bottom end of the receiving part, or may be that of the rodreceiving channel which is typically formed extending from the top endof the receiving part. Other inner walls are possible as well as long asengagement takes place within a perimeter of the receiving part and therelease operation is not directed into a space beyond such perimeter, inparticular by expansion. In embodiments described herein, the deviceperforms compression at its distal end when releasing the receiving inplace.

Consequently, an advantage arises in that it is not necessary to engagethe receiving part on any of its circumferential outer surfaces. This inturn allows to create narrower channels through the tissue of the humanbody to approach the bone under concern. Hence, aspects and embodimentsof the invention are particularly applicable in minimally invasivesurgery (MIS) and in situ assembly.

Engagement and/or disengagement is facilitated by radial expansion orcompression of the distal end portion of the collet, respectively. It isnot necessary to use the inner thread which is generally available atinner walls of receiving parts to facilitate locking by means of alocking screw. Instead, quick locking and releasing of the receivingpart with an improved tactile response becomes possible when placing thereceiving part onto the head.

With regard to the receiving part as proposed herein, only minorstructural changes have to be applied, if ally. For example, engagementfeatures may be provided at the inner walls of the rod receivingchannels. These may be protrusions, spring-like projections, noses,recesses, and similar means which allow a latching connection withcorresponding features of the device. Such engagement features may evenbe provided within a region of an inner thread—if present. According tospecific embodiments, even an inner thread might be considered toprovide corresponding latching features into which the engagementfeatures of the device expand during engagement.

A particularly advantageous embodiment becomes apparent in conjunctionwith an application to a bone anchoring device, wherein an inner cap isprovided within the receiving part, the inner cap clamping the head ofthe bone anchoring element thereby allowing a frictionally limitedmovement of the clamped bone anchoring element, when the device has notyet been finally locked. In this situation, the device allows aparticularly efficient placement method for the receiving part onto thehead.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantageous features and aspects will become more apparent from adetailed description of a specific embodiment taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 shows a perspective view of the device according to an embodimentof the invention with the collet in a locked position;

FIG. 2 same as FIG. 1, but in use just prior to a placement of thereceiving part onto the head and with the operation portion beingremoved;

FIG. 3 same as FIG. 1, but in a disassembled state;

FIG. 4A shows a cross section of the holding portion of the device shownin FIG. 1;

FIG. 4B same as FIG. 4A, but in an perspective view from a top;

FIG. 4C same as FIG. 4B, but seen from a bottom perspective;

FIG. 5A shows a cross section of a tube of the collet of the deviceshown in FIG. 3;

FIG. 5B shows an enlarged view of a proximal end of the tube shown inFIG. 5A;

FIG. 5C shows an enlarged view of the distal end portion of the collet;

FIG. 6A shows a perspective view of a proximal end portion of the colletaccording to the embodiment shown as in FIG. 3;

FIG. 6B same as FIG. 6A, but from a bottom perspective;

FIG. 6C same as FIG. 6A, but in a cross-sectional view;

FIG. 7A shows a perspective view of a plunger of the device shown inFIG. 3;

FIG. 7B shows an enlarged view of a tip portion of the plunger shown inFIG. 7A;

FIG. 8 shows a fixation device of the device shown in FIG. 1, formed asa follower pin;

FIG. 9 shows an operation portion of the device shown in FIG. 1;

FIG. 1 OA shows a cross-sectional view of a receiving part according toan embodiment of the invention, along with a top view thereof;

FIG. 10B same as FIG. 10A, but in a perspective view;

FIG. 11A shows a cross-sectional view of an inner cap according to anembodiment of the invention along with a top view thereof;

FIG. 11B same as FIG. 11A, but in a perspective view;

FIG. 12 shows in a cross-sectional view a first stage of a method ofusing the device according to the invention as shown in FIG. 1;

FIG. 13A shows in an enlarged perspective view the distal end portion ofthe collet and the receiving part in the same state as shown in FIG. 12;

FIG. 13B same as FIG. 13A, but in a second stage of advancing the distalend portion into the receiving part;

FIG. 13C same as FIG. 13B, but in a third stage wherein the distal endportion is engaged with inner walls of the receiving part;

FIG. 14 shows a cross-sectional view of the device in the same state asshown in FIG. 13C with the distal end portion of the collet being lockedby the plunger;

FIG. 15A shows in a partially cross-sectional view a fourth stage of themethod of using the device wherein the device is guided to a head of abone anchoring element in the locked state as shown in FIG. 14;

FIG. 15B same as FIG. 15A, but in a fifth stage with the head introducedand snapped into the inner cap;

FIG. 15C same as FIG. 15B, but in a sixth stage with the device drawnaway from the receiving part;

FIG. 16A same as FIG. 15C, but in a seventh stage with the distal endportion being unlocked;

FIG. 16B same as FIG. 16A, but showing the proximal portion of thedevice with the tensioned resilient member;

FIG. 16C shows a ninth stage of a method of using the device, whereinthe unlocked distal end portion of the collet is released from thereceiving part.

DETAILED DESCRIPTION

In the following, an embodiment of the device is described with respectto FIGS. 1-9, a corresponding embodiment of a receiving part with aninner cap is described with reference to FIGS. 10A-11B, and anillustrative example of a method of using the device and receiving partof both embodiments is given with reference to FIGS. 12-16C.

An overview of the device 1 for placing a receiving part onto a head ofa bone anchoring element is given in FIGS. 1-3. The device 1 accordingto this embodiment comprises a holding portion 2, a collet 3, anoperation portion 4, a plunger 5 and a resilient member 6. A fixationdevice 21 provided as a follower pin is supplied to the holding portionto establish a connection with plunger 5, and a cap-like proximal endportion 35 is provided to the collet 3 to allow attaching the operationportion 4 to a proximal end of the collet 3, and to provide a proximalabutment face 353 for the resilient member 6 as will be described below.

FIG. 1 shows the device 1 in a state, wherein the operation portion 4 isnot pressed, as a consequence of which the collet 3, or its distal endportion 31, respectively, is in a locked state, since a tip portion 52of plunger 5 extends into the distal end portion 31 as will be explainedin detail below.

Similarly, the device 1 as shown during use in FIG. 2 also is in alocked state, wherein, however, the operation portion 4 has been removedfrom the device 1. In a locked state, the receiving part 7 securelyadheres to the distal end portion of the collet 3 and may thus be safelyguided through an incision channel cut into the tissue (not shown)towards a head 91 of a bone anchoring element, which has already beenanchored in a pedicle of a vertebra shown in FIG. 2. The state shown inFIG. 2 substantially corresponds to that shown in FIG. 14 illustratingthe method of use, which will be discussed in detail below.

In what follows, an explanation of the constituent parts of the device 1is given first with respect to FIGS. 4A through 9.

The holding portion 2 is shown in FIGS. 4A-4C in cross-sectional, topand perspective views, respectively. The holding portion 2 of thisembodiment is of a substantially tubular shape with a textured profileat its outer surface to allow safe gripping by an operating staff. Inuse, the holding portion 2 is held with one hand, wherein a thumb mayfor example be used to press the operation portion 4. The holdingportion 2 includes an inner bore extending from a proximal end 27towards a distal end 28. A first bore portion 22 having a comparativelylarge diameter extends from the proximal end portion 27 and a secondbore portion 23 extends from the distal end portion 28. The second boreportion 23 has a smaller diameter as compared with the first boreportion 22. At the transition between the first bore portion 22 and thesecond bore portion 23 which both extend along a common longitudinalaxis, a shoulder 24 serving as a distal abutment face for one end of theresilient member 6 described below is formed.

A threaded bore 25 transversely extends through a wall of the holdingportion 2, and a further bore having a smaller diameter extends throughthe wall on an opposite side along the same axis as threaded bore 25.Bores 25, 26 are configured to receive fixation device 21 as shown inFIG. 8. More specifically, fixation device 21 has a threaded section 211configured to be threaded into the threaded bore 25, a narrowerunthreaded pin portion 213 configured to fit into the bore 26 of theholding portion 2, and a cylindrical middle portion 212 configured toslidably fit through an oblong aperture 38 of collet 3 described below.The fixation device 21 functions as a follower pin and fixes the plunger5 to the holding portion 2 such that both portions 2 and 5 together forma first unit of the device 1.

The collet 3 is depicted in FIGS. 5A and 5B with its proximal endportion 35 formed as a separate cap-like member depicted in FIGS. 6A-6C.The collet 3 is of substantially tubular shape (tube 37) and its outerdiameter is selected such as to slidably fit into the narrower secondbore portion 23 of holding portion 2. When being assembled, itslongitudinal axis Z is identical with that of the first and second boreportions 22, 23 of holding portion 2.

The collet 3 has a distal end portion 31 which is defined by two tongues311, 312 which in turn are formed by two opposite slots 32 extendingfrom a tip portion along the longitudinal axis Z up to a predetermineddistance from the tip. The tip portion 33 of the distal end portion 31is recessed from the overall cylindrical shape of the collet 3 andshaped such as to fit into the rod receiving channel and inner bore ofthe receiving part 7. Upon engagement of the distal end portion 31 withthe receiving part 7 an abutment face 331 of the collet 3 abuts on a topface of the receiving part 7. Moreover, each two rounded projections areformed as engagement features 34 on each of the tongues 311, 312 withinthe tip portion 33 of the collet 3. These projections extend in alateral or radial direction R from the collet 3.

The length of the slots 32 and the thickness of the walls of the collet3 are dimensioned and the material selected such that both tongues 311,312 are provided with resiliency such as to be expanded or compresseddepending on forces exerted during operation of the device 1.

For example, in this embodiment, the plunger 5 as shown in FIGS. 7A and7B is used to prevent compression and even to expand the tongues 311 and312 of collet 3. Plunger 5 is substantially rod-shaped and has acylindrical portion 51 having a diameter configured to slidably fit intoan inner bore 301 of collet 3. Plunger 5 further has a partiallycylindrical tip portion 52 having a smaller diameter as compared withthe cylindrical portion 51 and a conical portion 54 at a transitionbetween the cylindrical portion 51 and the tip portion 52. The diameterof the cylindrical part of tip portion 52 of plunger 5 is substantiallythe same as a diameter of a narrow diameter bore hole 314, which isprovided to extend from the shoulder 313 forming an end of inner bore301 of collet 3 up to the tip of the tip portion 33.

In this specific embodiment, tip portion 52 further includes a conicaltip portion 55 having a slightly increasing diameter larger than that ofthe cylindrical part of the tip portion 52.

Since the plunger 5 is configured to slide within the inner bore 301 ofcollet 3 the tip portion 52 of plunger 5 is allowed to enter the narrowdiameter bore 314 of the collet 3 wherein by virtue of the conical tipportion 55 having the larger diameter, the tongues 311, 312 are evenradially expanded in this embodiment. The length of the tip portion 52including the conical portion 55 substantially corresponds to the lengthof the narrow diameter bore 314. From the above, it becomes clear thatonce the tip portion 52 has entered the bore 314 of collet 3,compression of the tongues 311, 312 is impeded and even a slightexpansion is facilitated.

As explained above, the holding portion 2 and the plunger 5 form acommon unit in this embodiment. On the other side, collet 3 is allowedto move with respect to that unit along the longitudinal axis Z. Theextent of such movement is defined by the length of oblong hole 38through which the fixation device 21 extends as a follower pin in theassembled state. FIGS. 12 and 14 show respective states incross-sectional illustrations. More specifically, FIG. 12 shows a statein which the holding portion 2 and plunger 5 are moved towards aproximal direction and the collet 3 is moved towards a distal direction,which yields a state in which a tip portion 52 and conical tip portion55 of plunger 5 are retracted from narrow diameter hole 314 andshoulders 313. In this state, tongues 311, 312 may be compressed orexpanded thereby representing an unlocked position (“second releaseposition”). In this unlocked or release position, the fixation device 21is positioned at a proximal end of oblong hole 38 of collet 3. Theunlocked or release position allows an easy attachment or removal of thetongues 311, 312 to the receiving part 7.

On the contrary, FIG. 14 shows a second state, in which the collet hasbeen retracted towards the proximal direction and the holding portion 2and plunger 5 are uniformly moved forward. In this state, tip portion 52enters the narrow diameter bore 314 of collet 3 thereby preventingcompression of the tongues 311, 312. This state corresponds to a lockposition (“first lock position”) of the plunger 5 with respect to collet3. The first lock position may advantageously achieved, for example whenthe projections or engagement features 34 are engaged into respectivefeatures provided at the receiving part 7. Hence, a safe and secureengagement of the receiving part 7 may be accomplished. As can be seenfrom FIG. 14, the fixation device 21 is thereby positioned at theopposite distal end of oblong hole 38. Oblong hole 38 limits themovement of plunger 5 with respect to collet 3, and its ends toward theproximal direction and distal direction define, for example, the firstlock position and the second release position, respectively.

Returning to the description of the collet 3, a proximal end portion 35is achieved by a separate cap-like member shown in FIGS. 6A through 6C.Proximal end portion 35 includes a cylindrical tubular portion 352comprising an inner thread 351, that may be threaded upon an outerthread 36 provided at an end of collet 3 as shown in FIG. 5B. Proximalend portion 35 further has an inner bore 354 sized to receive therein apin-like projection 42 of operation portion 4 shown in FIG. 9. Thecylindrical portion 352 has the same outer diameter as that of thecylindrical tube portion 37 of collet 3. Further, a cap-like annularprojection 355 is provided whose diameter corresponds to that first boreportion 22 of holding portion 2. As a consequence, a surface is formedon its bottom side, which serves as a second abutment face 353 for asecond proximal end of resilient member 6.

As can be seen from FIG. 12 or 14, the resilient member 6 is held withinthe first bore portion 22 of holding device 2 and urges the proximal endportion 35 of collet 3 away from abutment face 24 of holding portion 2into the proximal direction. Thus, in a state where no forces areexerted onto operation portion 4, as shown in FIG. 14, the holdingportion 2 and plunger 5 are moved towards a distal direction, i.e.,towards the receiving part when being engaged, and the collet 3 isretracted towards the proximal direction together with its proximal endportion 35 and operation portion 4 which thus serve together as a secondunit of the device 1.

Next, an embodiment of the receiving part 7 suitable for interactionwith device 1 is described with reference to FIGS. 10A, 10B. Thereceiving part 7 includes a bore 700 extending from a first top end 72towards a second bottom end 73 wherein an opening 701 is formed at thebottom end 73. Adjacent to the opening 701, a seat 75 is formed whichdefines an accommodation space for accommodating a head receivingportion 82 of an inner cap 8 configured to clamp a head 91 of a boneanchoring element 91 such as that shown in FIG. 2. The bore 700 includesan inner wall 71, wherein at an upper portion of the inner wall 71, aninner thread for receiving a locking device (not shown) such as asetscrew is formed. An abutment feature 76 such as a recess is formed ina middle portion of the inner wall 71 which is designed to receivecorresponding abutment features 813, 814 of the inner cap 8 shown inFIGS. 11A and 11B.

Receiving part 7 also includes a rod receiving channel 74 which extendsfrom the first top end 72 and has substantially a U-shape. The rodreceiving channel 74 thus forms two legs and two inner walls 79 havingthe U-shape. As can be seen particularly from FIG. 10B, each tworecesses or engagement features 77 having rounded edges are formed in anupper portion of the inner walls 77. These engagement features 77 areconfigured and shaped to receive the engagement features 34 provided atthe distal end portion 31 of collet 3 of device 1. The recesses ofengagement features 77 similarly extend in a lateral directionperpendicularly to a longitudinal axis of the bore 700, whichlongitudinal axis is also coincident with the longitudinal axis Z ofcollet 3 in the assembled state. As a consequence of the lateral, orradial orientation expansion or compression of the distal end portion31, or of the tongues 311, 312, respectively, facilitates engagement ordisengagement.

It may be noted, that the receiving part 7 shown in FIGS. 10A and 10Bfurther comprises a classical engagement feature 78 provided at acircumferential surface 702 of the receiving part 7. That engagementfeature 78 allows engaging the receiving part 7 externally with anotherinstrument as known in the art.

An example of an inner cap 8 as part of the receiving part isillustrated in FIGS. 11A and 11B. The inner cap 8 includes a more orless cylindrical portion 81 and a substantially semi-spherical headreceiving portion 82. The head receiving portion 82 has resilientflanges 84 separated by slots 85, which together are configured toreceive and clamp the head 91 of bone anchoring element 9 in a snap-onfashion. In the clamped state, a resilient force is still exerted ontothe head 91 such as to provide friction to any pivoting movement of thebone anchoring element 9. Such feature provides an advantageous degreeof pre-locking for the bone anchoring device.

The cylindrical portion 81 has a diameter substantially corresponding tothe diameter of the bore 700 and, as explained above, abutment features813, 814 provided at the tips of legs 811, 812 may abut against edges ofrecess 76 to prevent falling off of the inner cap 8 from the bore 700.Moreover, the recess 76 is provided at a distance from the opening 701of receiving part 7, such that upon introduction of the head 9 throughopening 701, the inner cap 8 may move upward allowing the flanges 84 toexpand and to snap on the head 9. Upon final locking of the head 9, theinner cap 8 is urged toward the seat 75 such as to compress the flanges84 onto the spherical head 91 of bone anchoring element 9.

Next, operation of device 1 and receiving part 7, or its method of use,is explained with reference to FIGS. 12 through 16C. Therein, FIGS. 12through 14 reveal steps of engaging the receiving part 7, while FIGS.15A through 16C reveal steps placing and releasing the receiving part 7on the head 91 of the bone anchoring element 9, respectively.

FIGS. 12 and 13A show a first stage of the process before engagement ofthe receiving part 7. As can be seen in FIG. 12, the operation portion 4is already actuated (arrow Op) against the urging force of the coilspring of resilient member 6. Consequently, the unit comprisingoperation portion 4 and the collet 3 with proximal end portion 35 isadvanced towards a distal direction, or expressed reversely, the unitcomprising the holding portion 2 and plunger 5 is retracted towards aproximal direction. As a result, the tip portion 52 including theconical tip portion 55 of plunger 5 is retracted from the narrowdiameter hole 314 inside the distal end portion 31 of collet 3. Tongues311, 312 are then prevented from being resiliently compressed.

A second stage of the process is shown in FIG. 13B. The tip portion 33of distal end portion 31 is introduced into an inner space of thereceiving part 7 formed by bore 700 and rod receiving channel 74.Introduction is accomplished along the longitudinal axis Z of collet 3.As the cross-sectional profile of the tip portion 33 of collet 3corresponds to the cross section of the inner space of receiving part 7,the tip portion 33 initially may snugly fit into the inner space.However, the engagement features 34 protrude laterally outward from thetip portion 33 and eventually abut on top edges of the rod receivingchannel 74. Due to the rounded surface of engagement features 34,tongues 311, 312 deflect radially inward along direction R perpendicularto the longitudinal axis Z, i.e., are compressed towards each other (seearrow C).

As shown in FIG. 13C, the engagement features 34 latch into respectiverecesses of engagement features 77 thereby allowing the tongues 311, 312to expand again (see arrow E). FIG. 14 shows the same third stage of theprocess as shown in FIG. 13C, and it becomes apparent that releasing ofthe operation portion 4 leads to a retraction of the collet 3, or anadvancement of holding portion 2 with plunger 5, see arrow A, due to theurging force of resilient member 6. Thereby, the conical tip portion 55and the tip portion 52 of plunger 5 enters the narrow diameter hole 314of collet 3 thereby locking the engagement between collet 3 andreceiving part 7 (“first lock position”). More specifically, the tipportion 52 prevents any further compression such that engagementfeatures 34 cannot be released from engagement features 77. Moreover,further tightening is achieved by the conical tip portion 55 whichfurther expands the tip portion 33 and engagement features 34 intoengagement features 77 of receiving part 7.

In this situation, as shown in FIG. 14, the operation portion 4 may beremoved from device 1 as indicated by arrow Rem. Removal of theoperation portion 4 guarantees that no undeliberate release of thereceiving part 7 becomes possible during further steps of the method.This becomes possible, because the structure of the device 1 andreceiving part 7 allows an automatic release after placement of thereceiving part and upon a simple withdrawal movement of device 1 as willbe explained in the following.

FIG. 15A shows a fourth stage of the method. The assembly of device 1with engaged receiving part 7 is guided through an incision (not shown)in the tissue towards head 91 of bone anchoring element 9 whose shank 92has already been driven into the bone material of vertebra 100, seearrow G.

FIG. 15B shows a fifth stage of the method, wherein the head 91 isintroduced through the bottom opening 701 into the accommodation spaceof bore 700 and clicked into the head receiving portion 82 of inner cap8, see arrow Cl. Thereby, prior to being clicked into the head receivingportion 82 and clamped therein in a pre-lock fashion, the inner cap 8 ismoved upwards within bore 700 until projections 813 latch into recesses76 and abut on their upper edges. This abutment prevents the inner cap 8from moving further upwards. Having reached this position, flanges 84 ofhead receiving portion 82 are urged to deflect outwards and receive thehead 91 therein in snap-on fashion.

As shown in FIG. 15C, the collet 3 is then withdrawn from the boneanchoring element 9, see arrow W, as a result of which the inner cap 8moves downward within bore 700 (or reversely: the receiving part movesup) and is pressed against the seat 75 (or reversely: the seat ispressed against the inner cap) with the force of withdrawal. As aconsequence, the head 91 is clamped within inner cap 8 and the receivingpart 7 cannot further move up and cannot easily be released from theclamped state.

FIG. 16A shows a seventh stage of the method wherein, as shown in FIG.16B, further withdrawal leads to a compression of resilient member 6,because it is the holding portion 2 that is effectively drawn up by theoperating staff and not the collet 3. Once the head 91 and inner cap 8are in a clamped state as shown in FIG. 15C, the collet 3 cannot befurther drawn up and the holding portion 2 is moved with respect tocollet 3 under increasing tensioning or biasing force exerted on thecoil spring of resilient member 6, see arrow B. This in turn leads to aretraction (see arrow F) of plunger 5 and conical tip portion 55 fromthe distal end portion 31 of collet 3. This position of plunger 5corresponds to a released or unlocked position with respect to thedistal end portion 31, and further withdrawing the device 1 allowscompression of the tongues 311, 312 (see arrow C in FIG. 16A) andtherefore release of receiving part 7. As noted above, upon drawing upthe holding portion, the resilient member is tensioned with anincreasing force. Thereby, the resilient member 6 is configured to betensioned by an amount of force in a state, in which the plunger 5releases the distal end portion 31, which amount of force is less than aclamping force exerted by the flexible head receiving portion 82 of theinner cap 8. Hence, it is assured that the receiving part is releasedbefore the head unclamps from inner cap 8, even if it would not bepressed against seat 75 and thus locked.

As shown in the eighth stage, revealed in FIG. 16C, the collet 3 maydisengage from the receiving part 7 (see arrow D) which is thus safelyplaced onto the head 91 of bone anchoring element 9. Simultaneously, asforces are not exerted any more onto device 1, the collet 3 withindevice 1 is immediately retracted towards the proximal direction againunder the urging force of resilient member 6 with respect to holdingportion 2, such that device 1 returns into its initial locked state.

In the state achieved so far, the receiving part is pre-locked, whichmeans that by virtue of friction created between the head receivingportion 82 and the clamped head 91, the receiving part has given posturewith respect to the bone anchoring element 9, which may, however, easilybe repositioned by hand or an instrument. Further possible steps theninclude supplying a spinal rod (not shown) to the receiving part,wherein the spinal rod is inserted into the rod receiving channel 74.Moreover, a locking screw (not shown) can then screwed into the innerthread at the inner wall 79 of the receiving part 7, which locks thespinal rod, which in turn presses onto the V-shaped groove within thecylindrical portion 81 of the inner cap 8 such as to firmly and finallylock the receiving part 7 and head 91.

It may be noted that various modifications may be applied to aspects andembodiments of the invention which may be considered to come within thescope of the appended claims. In the above embodiments, metal materialssuch as titanium, or nickel titanium alloys or Nitinol or otherbody-compatible metals are employed for each of the components. Howeverother materials such as plastic materials, or PEEK, etc. may also beused.

Moreover, in the above embodiment, a receiving part employing an innercap having a specific head clamping function is used. Nevertheless,other structures of receiving parts having pressure elements or otherinner caps may also be used.

In the above embodiments, expansion of tongues is used to engage withengagement features provided at a receiving part. However, it is alsocontemplated that movable engagement parts may be provided at a tip of ashaft which provide an expanding movement within an inner space at areceiving part upon engagement.

1. A device for placing a receiving part of a bone anchoring device ontoa head of a bone anchoring element, comprising: a holding device, acollet having a longitudinal axis and being held by the holding device,wherein the collet includes a distal end portion configured to beflexibly expanded and/or compressed in a radial direction perpendicularto the longitudinal axis, wherein an engagement feature is provided atan outer contour of the distal end portion of the collet configured toengage a portion of an inner wall formed in a rod receiving channel or abore of a receiving part.
 2. The device of claim 1, further comprising aplunger configured to selectively lock and release the distal endportion of the collet at the receiving part, when the engagement featureengages the portion of the inner wall formed in the receiving part. 3.The device of claim 2, wherein the collet is configured to be movablewith respect to the plunger in a direction along its longitudinal axisbetween at least a first lock position, in which the distal end portionof the collet is prevented by a portion of the plunger from beingcompressed, and a second release position in which the distal endportion may be resiliently compressed.
 4. The device of claim 2, whereinthe plunger is fixedly coupled to the holding device.
 5. The device ofclaim 2, wherein the collet is movably held by the holding device andhas a tubular shape; and the plunger has a rod-shape and at leastpartially extends through the collet.
 6. The device of claim 5, whereinthe plunger is coupled to the holding device via a fixation deviceextending though an oblong aperture formed in the tubular-shaped collet.7. The device of claim 2, further comprising: a resilient member, whichis coupled between the holding device and a proximal end portionprovided at the collet so as to urge the collet into a proximaldirection in order to establish the first lock position.
 8. The deviceof claim 7, wherein the plunger has a tip portion, which is configured,in the first lock position, to enter the distal end portion of thecollet such as to prevent compression thereof.
 9. The device of claim 8,wherein the tip portion of the plunger further comprises a tapered orconical portion configured to further expand the distal end portion ofthe collet in addition to preventing compression.
 10. The device ofclaim 7, further comprising an operation portion, which is removablyconnected, fixed to, or integrally formed with the proximal portionprovided at the collet configured to allow an operator to move thecollet with respect to the holding device and plunger against an urgingforce of the resilient member to establish the second release position.11. The device of claim 7, wherein the receiving part of the boneanchoring device further includes the bore extending from a first end toa second end of the receiving part, the rod receiving channel extendingfrom the first end, and a seat providing an accommodation space for ahead of the bone anchoring element is formed at the second end, whereinan inner cap is movably disposed within the accommodation space, whichinner cap includes a flexible head receiving portion configured toresiliently clamp the head, and the resilient member is configured to betensioned by a force in order to achieve a state, when the plungerreleases the distal end portion, which force is less than a clampingforce exerted by the flexible head receiving portion of the inner cap.12. The device of claim 1, wherein the distal end portion of the colletincludes two or more flexible tongues, which are configured to beflexibly expanded and/or compressed in a radial direction perpendicularto the longitudinal axis.
 13. The device of claim 1, wherein theengagement feature is a protrusion or latching recess, which isconfigured to latch into a corresponding latching recess or protrusion,respectively, provided at the inner wall of the receiving part.
 14. Thedevice of claim 13, wherein two or more of the engagement features areprovided.
 15. A receiving part for connecting a bone anchoring elementhaving a head and a shank to a spinal rod, comprising: a bore extendingfrom a first end to a second end of the receiving part and comprising aninner wall, a rod receiving channel extending from the first end andcomprising an inner wall, an opening of the bore provided at the secondend and being configured to allow introducing the head into the bore,and a seat formed adjacent the opening and providing an accommodationspace for the head of the bone anchoring element, wherein the inner wallof the rod receiving channel or the inner wall of the bore comprises anengagement feature configured to engage a corresponding engagementfeature of a device for placing a receiving part onto a head of a boneanchoring element.
 16. The receiving part of claim 15, furthercomprising an inner cap comprising a flexible head receiving portionconfigured to resiliently clamp the head, the inner cap being movablydisposed within the accommodation space.